THE EFFECT OF TURBULENCE ON THE COLLISION RATES OF SMALL CLOUD DROPS

The significance of the influence of turbulence on collisions and coal escence of small cloud droplets is still an outstanding problem. In pa rticular, the growth of droplets in the radius range from 10 to 15 mu m is not well understood. The present research examines whether or not turbulence affects the growth rate of such small drops by simulating trajectories of two hydrodynamically interacting droplets in a turbule nt field. The trajectories were calculated with a model based on linea r Stokes hydrodynamics. Turbulence was modeled in the form of random F ourier modes with both the space and time spectra prescribed, Both spe ctra were characterized by Kolmogorov scaling. The space spectrum was modeled in the inertial and dissipation subranges. On the basis of sca le analysis, only small-scale time variations were allowed, and the so -called Eulerian-Lagrangian time spectrum was applied. The results sho w that most collision rates increase moderately in a turbulent flow ch aracterized by rates of energy dissipation of the order of 1, 10, and 100 cm(2) s(-3).